1. Field of the Invention
The present invention concerns the reduction of background noise picked up by a first microphone spoken into by a first person. More particularly, the present invention concerns reducing background noise in telephone conversations, where an agent is working in a noisy environment.
2. Description of the Related Art
Call centers, where many agents are calling many persons simultaneously, are widely employed throughout several industries. For example, several stockbrokers in close proximity to each other call many stockholders simultaneously. Telemarketers and pollsters often sit in side-by-side cubicles and call households. Often dozens of emergency personnel sit side-by-side in a 911-call center and receive urgent requests for emergency services.
A common problem in such call centers is that background noise can be distracting and cause miscommunications. The background noise is primarily due to the voices of the other agents in the call center who are simultaneously communicating on other unrelated telephone calls. Moreover, sensitive information can sometimes be heard in the background conversations, such as in the case of the stockbrokers or 911-call center instances.
Another source of background noise problems in such situations can be mechanical sounds emanating from nearby equipment, such as printers, photocopiers, automatic doors, elevators, and HVAC systems. Such sounds may also interfere with a conversation and lead to miscommunications, distractions and annoyances.
As an example with reference to FIG. 1, let agent A be a call-center agent of interest who is engaged in a telephone call with customer A. The call transpires between the agent A and the customer A via a headset on agent A, a wired connection to a private business exchange (PBX) 20, a wired connection to a public switched telephone network (PSTN) 22 and a wired connection to a headset, handset or speakerphone of the customer A.
Speech from other agents B . . . N, near agent A, may arrive at agent A's microphone and be transmitted to customer A. This extraneous speech is not related to the conversation occurring between agent A and customer A and degrades the quality of the conversation occurring between agent A and customer A. Likewise, if a sheet-feeding photocopier 2 or rattling heating vent 4 is close to agent A, those extraneous sounds may also enter into agent A's microphone and be an annoyance to the conversation, as perceived by customer A.
One attempt to address these problems in the background art has been the employment of noise-canceling headsets in a call center. A noise-canceling headset 10 employed by an agent A in a call center, according to the background art, is illustrated in FIG. 2. The headset 10 includes a primary microphone 12 directed toward the mouth of agent A, wearing the headset 10. A secondary microphone 14 is directed away from the mouth of agent A. The secondary microphone 14 is intended to pickup the extraneous noises EN in the environment surrounding the headset 10, such as the conversations of other nearby agents B, C . . . N and equipment noises in the environment. The primary microphone 12 is intended to pickup the voice of agent A.
The outputs of the primary and secondary microphones 12 and 14 are connected to a digital signal processor (DSP) 16 in the headset 10. The DSP 16 analyzes the extraneous noise EN signals received from secondary microphone 14 and attempts to modify the voice signal received from the primary microphone 12 by removing the extraneous noise EN sound signals. This modification is accomplished by adaptive signal processing. Adaptive signal processing systems and methods to remove unwanted noise from a sound signal are known in the art and would be understood by those of ordinary skill in the art. See for example, Widrow and S. D. Stearns, Adaptive Signal Processing, Prentice-Hall, 1985.
The modified voice signal 15 is output by the DSP 16 and sent to the private business exchange (PBX) 20 via a wired connection 18. The modified voice signal 15 may also be sent to speakers 19 of the headset 10 for the benefit of agent A, wearing the headset 10. The PBX 20 sends the modified voice signal to the public switched telephone network (PSTN) 22 for transmission to an outside party of the call, such as customer A. Each of agents B, C . . . N would wear a similar noise-canceling headset 10 and be connected to PBX 20 and could hold conversations with other customers, as illustrated in FIG. 2.
The solution in accordance with the background art has enjoyed limited success. It is believed that such a secondary microphone and DSP system provides a reduction of the extraneous noise EN on the order of about 6 dB. A 6 dB reduction of the extraneous noise EN is certainly an improvement over the typical headsets, without noise cancellation capability.
However, the Applicant has appreciated several drawbacks to the solution in accordance with the background art. First, a 6 dB reduction in noise is not dramatic or particularly significant. While it is an improvement, the customer may still overhear other conversations in the call center, and be distracted and annoyed by other background noises, which can still be quite loud, even after a 6 dB reduction.
Second, the DSP 16 will introduce a level of distortion into the modified voice signal transmitted by the DSP 16 to the customer. The distortion is primary the result of the close proximity of the secondary microphone 14 to the wearer of the headset 10. In other words, even through the secondary microphone 14 is directed away from the mouth of the wearer of the headset 10, the voice of the wearer will, to some extent, enter into the secondary microphone 14. After all, the voice of the wearer is usually the most intense sound source in the proximity of the secondary microphone 14, and the directional quality of the secondary microphone 14 is not perfect.
Therefore, the DSP 16 will receive a certain level of the voice of the wearer through the secondary microphone 14 and may have difficulty in accurately distinguishing the extraneous noise EN from the wearer's voice signal. As a result, the DSP 16 will modify the voice signal coming from the primary microphone 12 by removing the noise signal (which includes the extraneous noise EN and the voice signal), which will degrade the quality of the agent's voice, as perceived by the customer A.
Another drawback is that the DSP 16 of the headset 10 must be miniaturized to be conveniently located within the framework of the headset 10. Therefore, the DSP 16 is typically of a custom design and has less processing power than a full-size processor, as used in common computers. Also, it is difficult, and typically prohibitively expensive, to upgrade the software of the DSP 16 or to replace the DSP 16 with an upgraded processor, as the technology improves over time.
Another drawback is that a power source 17 is required by the DSP 16. The power source 17 is typically a battery and must be recharged and periodically replaced. Also, the power source 17, DSP 16, and secondary microphone 14 add to the weight of the headset 10, which adds to the discomfort of the wearer.
Another drawback is the cost and complexity of the headset 10. Each headset 10 must include one or more secondary microphones 14. Also each headset 10 must include the DSP 16 and the power source 17. Therefore, the cost of the headset 10 is much higher than the cost of a simple headset without noise-cancellation circuitry, and the repair cost is likewise much higher. It is certainly feasible that the costs of high-quality noise-canceling headsets 10 would be several hundreds of dollars each. Therefore, for a call center (telemarketing, stock broker facility, 911-center etc.) employing perhaps one hundred agents, the expense and maintenance of such noise-canceling headsets could be very expensive, in the hundred thousand dollar range.